1. Field of the Invention
Typically, an automobile air conditioning system has an air-bypass passage which allows air to bypass a heater core and flow into a vent outlet so as to direct air, which has been passed through an evaporator, towards the heads of car occupants. Supplying cool air to a region around the head or heads of an occupant or occupants, while heating is in operation, often provides the occupant with a comfortable air conditioned state. The provision of such an air-bypass passage is intended to produce a comfortable air conditioned state known as a "cool head-warm feet" air conditioned state. Clearly, in such a state, the occupants of the vehicle feel cool around their heads and warm around their feet. The air-bypass passage is accompanied by a bypass door, which opens and closes so as to change a cross-sectional area of the air-bypass passage and thereby blow off air, desirably regulated in temperature and quantity, towards the occupants' heads. This provides the occupants with a comfortable air conditioned feeling.
In particular, the bypass door is conventionally controlled to fully open and blow off cool air towards the head region when the temperature of blowing air is higher than a given temperature of blowing air and when an interior of the vehicle is at temperatures lower or higher than a selected air conditioning temperature. Such an air conditioning system is known from, for example, Japanese Unexamined Patent Publication No. 63-34216.
2. Description of Related Art
In the air conditioning system described in the Japanese publication mentioned above, because the air-bypass door always opens fully whenever both of the conditions referred to are established, a large quantity of cool air often blows off at once towards the head region of the occupant or occupants, so as to decrease suddenly the temperature of air in this region, particularly when the exterior of the vehicle is at low temperatures. Consequently, in this condition, the occupants may become uncomfortable. This is also true even if the air-bypass door is intentionally opened.
Automatic continuous controlling of the bypass door according to changes in temperature of air around the head region could be considered. However, in this case, it is impossible to increase and decrease the quantity of bypass air according to passenger desire.